Shifting device and gear unit

ABSTRACT

A shifting device for a transmission unit of a vehicle, in particular a vehicle that is driven by muscle force. The transmission unit has a first shaft, which is formed as a hollow shaft, on which a plurality of free gears is mounted. The free gears are in engagement with a corresponding plurality of gearwheels, which are mounted on a second shaft, wherein the free gears are connectable to the first shaft by means of selecting devices. The selecting devices can be actuated by means of a camshaft arranged coaxially in the first shaft, wherein the camshaft is connected to a driving device in order to be rotated relative to the first shaft to actuate the selecting devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 13/525,493filed Jun. 18, 2012, now U.S. Pat. No. 8,628,447, which is aContinuation application of International patent application PCT/EP2010/069996, filed Dec. 16, 2010, which claims the priority of Germanpatent application DE 10 2009 060 484.7, filed Dec. 18, 2009.

BACKGROUND OF THE INVENTION

The present invention relates to a shifting device for a transmissionunit of a vehicle, in particular a vehicle that is driven by muscleforce, having a first shaft, which is formed as a hollow shaft, on whicha plurality of free gears is mounted, wherein the free gears are inengagement with a corresponding plurality of gearwheels, which aremounted on a second shaft, wherein the free gears are connectable to thefirst shaft by means of selecting means, wherein the selecting means canbe actuated by means of a camshaft arranged coaxially in the firstshaft, wherein the camshaft is connected to driving means in order to berotated relative to the first shaft to actuate the selecting means.

The present invention furthermore relates to a gear unit for a vehicle,in particular a vehicle that is driven by muscle force, having a firstshaft, on which a plurality of first gearwheels is mounted, a secondshaft, on which a corresponding plurality of second gearwheels ismounted, wherein the second gearwheels are in engagement with thecorresponding first gearwheels.

The present invention furthermore relates to a vehicle having a frameand a gear unit, which has a first shaft, on which a plurality of firstgearwheels is mounted, and a second shaft, on which a correspondingplurality of second gearwheels is mounted, wherein the second gearwheelsare in engagement with the first gearwheels, wherein the first and thesecond shaft are mounted in a gear case which at least partiallysurrounds the gear unit.

Gear units of this kind are used to provide different transmissionratios for driving a vehicle, in particular a vehicle that is driven bymuscle power.

There are fundamentally three types of gear shift for vehicles orbicycles driven by muscle power, namely derailleurs, hub gears andbicycle transmissions.

The derailleur has remained essentially unchanged in the last fewdecades. In this case, a chain transmits the motive power from a crankto the rear axle of the bicycle, and a set of sprockets comprising up to11 sprockets is mounted on the rear axle, between which it is possibleto shift by means of a frame-mounted derailleur for controlling thechain. Moreover, most bicycles are additionally fitted with a shiftmechanism at the chain wheel associated with the bottom bracket. In thiscase, up to three chain wheels are mounted on the crank, and it ispossible to shift between them by means of a front derailleur attachedto the frame. Derailleurs of this kind provide up to 30 gears, although,by the nature of the system, many of the gears are redundant and somegears are of limited or no use due to high frictional losses caused bydiagonal chain alignment.

The disadvantage with the derailleur principle is that, in addition tothe large number of redundant gears and the frictional losses, thecomponents are exposed and are therefore directly subject toenvironmental influences such as water and dirt and can very easily bedamaged by impact.

The second type of commercially available bicycle shift mechanism is thehub gear. In contrast to the derailleur, this is understood to mean agear mechanism built into the hub casing of the rear axle. A hub geargenerally has no external shift components and is therefore notsusceptible to impact and less exposed to environmental influences thanthe derailleur. A hub gear of the kind known from DE 197 20 794 A1, forexample, can currently provide up to 14 gears. The disadvantage with theprinciple of the hub gear in the rear axle is that the weight of therotating masses is increased, and, in the case of bicycles with rearwheel suspension, that the unsprung mass relative to the total weight isincreased. Moreover, the center of gravity of the bicycle shifts in thedirection of the rear axle, and this has a disadvantageous effect on theride characteristics of the bicycle, especially in the case of mountainbikes with rear wheel suspension.

A hub gear of this kind is known from EP 0 383 350 B1, for example, inwhich two planetary mechanisms are arranged coaxially with a hub fixedwith respect to a housing, wherein the input shaft can be connected toplanet carriers, and the sun gears of the planetary mechanism can beconnected for conjoint rotation, by means of a rotatable shiftingdevice, to the hub fixed with respect to the housing in order to providedifferent transmission ratios in the overall gear mechanism. Thedisadvantage with this gear mechanism is that the construction of theoverall gear mechanism is complex and is therefore, on the one hand,expensive to produce and, on the other hand, has a high weight due tothe large number of components while providing only a small number ofachievable gears.

The third variant of bicycle shift mechanisms are the bicycletransmissions mounted in the region of the bottom bracket or bottombracket transmissions. This type of bicycle shift mechanism is never oronly very rarely found on commercially available bicycles. In general,bicycle transmissions of this kind have the advantage over conventionalderailleurs or hub gears that they do not have any exposed componentsand are therefore protected from impact and environmental influences,and furthermore shift the center of gravity of the bicycle to the centerwhile, at the same time, reducing the total unsprung mass. This isparticularly advantageous in mountain bike sport. One technicalchallenge with bicycle transmissions of this kind is to provide acompact construction combined with a large number of selectable gears.

U.S. Pat. No. 5,924,950 A discloses a bicycle transmission having aninput shaft, on which a plurality of drive gears is mounted, and acountershaft, on which a corresponding number of selectable driven gearsis mounted. The selectable gears on the countershaft are selected bymeans of a plurality of axially movable shift pins and freewheelsarranged in the countershaft, wherein the countershaft is connected to apinion as an output member of the vehicle transmission via a planetarymechanism. The pinion is connected to the sun gear of the planetarymechanism via a clutch, and the annulus of the planetary mechanism canbe braked by means of a Bowden cable. By means of this bicycletransmission, it is possible to obtain 14 gears. The disadvantage withthis system is the large axial extent of the design and the relativelysmall number of gears that can be obtained, namely 14.

WO 2008/089932 A1 furthermore discloses a gear unit for bicycles, inwhich a high number of gears can be obtained using two countershafts andan additional transmission subsection, by multiplying the individualgears of the two transmission subsections, and, at the same time, acompact construction can be achieved. The disadvantage with this gearunit is that a camshaft is moved axially to select the free gears and,as a result, the axial extent of the transmission design is great.

EP 1 982 913 A1 discloses a transmission for bicycles in which freegears are mounted on an input shaft of the transmission and can beconnected selectively to the input shaft by means of a sleeve mounted inthe shaft, wherein the sleeve is turned relative to the input shaft bymeans of two planetary mechanisms in order to select the free gears. Theplanetary mechanisms are arranged coaxially with the input shaft and areactuated by means of a selector shaft, which is offset parallel to theinput shaft and is connected to a Bowden cable. The selector shaft isconnected for conjoint rotation to a planet carrier of one of theplanetary mechanisms by a spur gear mechanism in order to transmit therotation of the selector shaft to the sleeve. The disadvantage with thistransmission is that the additional rotation is transmitted to theplanetary mechanism by means of the selector shaft which is offset inparallel, thereby requiring a large amount of installation space for thegear unit.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved shifting device and an improved gear unit for a vehicle, inparticular a vehicle that is driven by muscle force, which, inparticular, is of more compact construction, permits a large number ofgears and simultaneously a reduced total weight, and is simple tooperate, as compared with the known shifting devices and gear units.

In the context of the invention, vehicles driven by muscle force aretaken to be vehicles which are driven exclusively by muscle force or inwhich muscle force in combination with a power unit, e.g. an internalcombustion engine or an electric drive, is used to drive the vehicle.

According to a first aspect of the invention, this object is achieved,in the shifting device mentioned at the outset, by virtue of the factthat the driving means have a rotational speed superimposition gearunit, which is arranged coaxially with the first shaft, wherein a secondcamshaft is arranged coaxially in the first shaft in order to connect aplurality of second free gears, which are mounted on the first shaft, tothe first shaft by means of selecting means.

According to a second aspect of the invention, the abovementioned objectis furthermore achieved in the shifting device mentioned in the outsetby virtue of the fact that the driving means have two planetary gearunits, wherein planet carriers of the planetary mechanisms are connectedto one another.

According to a third aspect of the invention, the abovementioned objectis furthermore achieved in the shifting device mentioned at the outsetby virtue of the fact that the camshaft can be connected to the firstshaft by means of latching means in at least one rotational position.

According to a fourth aspect of the invention, the abovementioned objectis furthermore achieved in the shifting device mentioned at the outsetby virtue of the fact that a second camshaft is arranged coaxially inthe first shaft and can be rotated relative to the first shaft by meansof a tappet of the first camshaft.

According to a fifth aspect of the invention, the abovementioned objectis furthermore achieved by virtue of the fact that a spring sleeve isarranged in the first shaft, surrounding the camshaft circumferentially,in order to preload the selecting means with a spring force.

According to a sixth aspect of the invention, the abovementioned objectis furthermore achieved in the gear unit mentioned at the outset byvirtue of the fact that at least one of the second gearwheels can beconnected nonpositively to the second shaft by means of a clutch.

According to a seventh aspect of the invention, the abovementionedobject is furthermore achieved in the vehicle mentioned at the outset byvirtue of the fact that the gear case is connected to the frame by meansof damping members in order to mechanically decouple the frame at leastpartially from the gear unit.

According to one embodiment of the invention, a transmission isprovided, having a shaft, which is designed as a hollow shaft, on whicha plurality of free gears is mounted, which can be connected to thehollow shaft by means of selecting means, wherein the selecting meanscan be actuated by means of a rotatable camshaft, wherein the free gearsform sun gears of planetary gearsets, and planet carriers and/or ringgears of the planetary gearsets are connectable to the shaft and/or toan output shaft. It is thereby possible to obtain additional gear stagesin the transmission.

In this arrangement, the output shaft is preferably mounted coaxiallywith the shaft. A particularly compact construction is possible as aresult. It is preferable if the planet carrier can be connected to theshaft by means of selecting means, wherein the selecting means can beactuated by means of the rotatable camshaft. This makes it possible todispense with an additional camshaft or further actuating means.

One advantage of the first aspect of the shifting device according tothe invention is that the rotational speed superimposition gear unit,which is arranged coaxially with the shaft, and the second camshaft makeit possible to achieve a compact gear unit with a large number of gears.

One advantage of the second aspect of the shifting device according tothe invention is that the combination of two rotational speedsuperimposition gear units makes it possible to achieve the rotation ofthe camshaft in the first shaft with few components and hence that thetotal weight of the transmission is limited.

One advantage of the third aspect of the invention is that the latchingmeans for accurate positioning of the camshaft relative to the firstshaft within the transmission make it possible to dispense with externalindexing shift levers, which are expensive and simultaneouslyvulnerable.

One advantage of the fourth aspect of the invention is that it ispossible to dispense with two independent shift levers, making shiftingparticularly convenient. In this arrangement, the driving means can bemechanical, electric and/or hydraulic driving means.

One advantage of the fifth aspect of the invention is that the selectingmeans can be reliably preloaded by means of a simple-to-fit springsleeve, thus enabling the outlay on assembly to be considerably reduced.

One advantage of the sixth aspect of the invention is that the torquewhich can be transmitted is limited, and this enables the gearwheels tobe designed for a lower permissible maximum torque, thereby allowing theweight and overall size of the gear unit to be reduced.

One advantage of the seventh aspect of the invention is that vibrationand noise generated by the gear unit cannot be transmitted to the frameof the vehicle and that resonant vibration is attenuated, therebyallowing an improvement in ride comfort.

In the case of the first aspect of the invention, the second free gearsare preferably in engagement with a corresponding plurality ofgearwheels, which are mounted on a third shaft, wherein the second freegears form gear pairs of a second transmission subsection with thegearwheels.

It is generally preferred if the rotational speed superimposition gearunit is arranged at one axial end of the shaft.

A construction which is particularly compact in the radial direction isthereby possible.

A ring gear of the second of the planetary gear units is preferablyconnected to actuating means.

This enables an additional rotation from the outside to be transmittedto the camshaft in a simple manner.

The actuating means are preferably arranged coaxially to the firstshaft.

This arrangement enables a rotation from the outside to be imparted tothe camshaft by structurally simple means, thereby allowing aparticularly compact construction of the transmission.

The actuating means preferably have a cable pulley, which is mountedcoaxially with the first shaft. The cable pulley is preferably connectedrotationally fixed to the ring gear. In a special embodiment, the cablepulley is formed integrally with the annulus. A particularly lightconstruction of the actuating means is thereby possible.

A sun gear of the first planetary gear unit is preferably connected tothe camshaft for conjoint rotation.

This makes it possible to connect the planetary mechanism to thecamshaft without additional design outlay, thereby allowing a generallycompact construction.

It is furthermore preferred if a sun gear of the second planetarymechanism is connected rotationally fixed to the first shaft.

This enables the rotation of the first shaft to be transmitted to theplanetary mechanism and the camshaft with little design outlay.

It is furthermore preferred if the rotation speed superimposition gearunit is designed in such a way that the camshaft rotates in synchronismwith the first shaft. In this case, the rotation speed superimpositiongear unit is designed in such a way that, in normal operation, when thering gear of the second planetary mechanism is not rotating, i.e. is notselected, the camshaft rotates in synchronism with the first shaft.

As a result, the shift states set are retained while the first shaftrotates and the ring gear remains stationary.

In the case of the third aspect of the invention, it is preferred if thelatching means have a first latching member, which is connectedrotationally fixed to the camshaft, and a second latching member, whichis connected rotationally fixed to the first shaft.

This enables a certain fixed shift state to be set without externallatching means.

It is furthermore preferred if the latching means are arranged coaxiallywith the first shaft.

As a result, the latching means can be implemented without anyadditional space requirement, thereby making possible a compactconstruction.

It is furthermore preferred if at least one of the latching members isarranged in the first shaft.

This makes it possible to achieve a compact gear unit constructionbecause unused installation space in the first shaft is utilized.

It is furthermore preferred if the latching means have at least one noseand at least one groove in order to latch in the at least one rotationalposition.

As a result, the latching means are particularly robust and reliablebecause they can be implemented without additional moving parts.

It is furthermore preferred if at least one of the latching members isspring-mounted so as to be axially movable.

On the one hand, this ensures that the latching means connect the firstshaft and the camshaft in one rotational position and, at the same time,the latching connection can be released from the rotational positionwithout an additional mechanism by applying a torque.

It is furthermore preferred if the second camshaft can be rotatedrelative to the first shaft by means of a tappet of the first camshaft.

This makes it possible to dispense with a second, independent shiftlever, thereby making control of the shifting device particularly simpleand convenient.

In the invention, it is preferred if the second camshaft is connectableto the first shaft in at least one rotational position by means oflatching means.

This makes it possible to obtain a set shift state of the secondtransmission subsection by simple means, without external actuation,thereby also preventing unintentional shifting.

It is furthermore preferred if the second camshaft is spring-mounted soas to be axially movable.

It is thereby possible to ensure that the latching means latch with thefirst shaft in the predefined rotational position and can be releasedfrom the rotational position by applying a torque.

It is furthermore preferred if the latching means have at least one noseand at least one groove in order to latch in the at least one rotationalposition.

As a result, the latching means are particularly robust and reliablebecause it is possible to dispense with additional moving parts.

It is furthermore preferred if the tappet has a movable tappet element,which slides on a sliding section, which is connected rotationally fixedto the first shaft.

As a result, the second camshaft can be turned through a certain angleof rotation relative to the first shaft at certain rotational positions,and simple, logical linking of the two camshafts can be achieved.

It is furthermore preferred if the tappet element is mounted in a recessof a tappet member so as to be movable in a radial direction.

As a result, the tappet element can be brought into releasableengagement with the second camshaft with little design outlay and asmall space requirement.

It is furthermore preferred if the tappet member is connectedrotationally fixed to the first camshaft.

As a result, the rotation of the first camshaft can be transmitted tothe tappet and thus logical linking of the shifting of the twotransmission subsections can be achieved.

It is furthermore preferred if the sliding section has at least one cam,by means of which the tappet element can be moved in a radial direction.

This enables the second camshaft to be taken along and rotated, morespecifically by a particular angle of rotation, at a predeterminedrotational position of the first camshaft relative to the first shaft.

It is furthermore preferred if the tappet element can be brought intoengagement with the second camshaft in order to connect the firstcamshaft to the second camshaft rotationally fixed.

This enables the rotation of the first camshaft to be transmitted to thesecond camshaft without actuation from outside.

It is furthermore preferred if the selecting means are designed asselectable freewheels.

This enables the free gears to be connected rotationally fixed to thefirst shaft by simple and compact selecting means.

The selecting means preferably have selector pawls, which can be broughtinto engagement with internal toothing of the free gears.

This makes it possible to obtain actuatable freewheels which can accepta high torque because they transmit force in a tangential direction fromthe free gear to the shaft.

It is furthermore preferred if the camshafts have actuating sections, bymeans of which the freewheels can be actuated.

This enables the freewheels to be brought into engagement with the freegears by means of a measure of simple design.

It is furthermore preferred if the camshafts are designed in such a waythat freewheels of two successive gears stages can be brought intoengagement simultaneously with the free gears.

This makes it possible to obtain a power shift transmission because thefreewheel of the higher gear is brought into engagement with thecorresponding free gear while the freewheel of the lower gear isfreewheeling. Moreover, idle rotation is avoided.

In the case of the fourth aspect of the invention, it is preferred ifspring elements, each assigned to one of the selecting means, are formedon the spring sleeve.

This makes it possible to provide low-cost spring elements for theselecting means that can be mounted easily in the first shaft.

It is preferred if the spring elements are formed integrally with thespring sleeve.

This makes it possible to manufacture the spring elements atparticularly low cost.

In the case of the fifth aspect of the invention, it is preferred if theclutch connects the corresponding gearwheel nonpositively to the secondshaft up to a predetermined torque.

As a result, the gearwheels can transmit a torque to the second shaftwithout restriction up to a certain magnitude.

It is furthermore preferred if the gearwheel slides on the second shaftat a torque above the predetermined torque.

This makes it possible, by simple means, to avoid overloading of thegearwheels and accordingly to design the gearwheels for lower loads,thereby making lighter construction possible.

It is furthermore preferred if the predetermined torque is adjustable.

This enables the gear unit to be matched specifically to certain loadstates.

The second shaft is preferably an input shaft of the gear unit. Thismakes it possible to limit the torque introduced into the gear unit.

Needless to say, the features which are mentioned above and those whichwill be explained below can be used not only in the respectivelyindicated combination but also in other combinations or in isolationwithout exceeding the scope of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Illustrative embodiments of the invention are shown in the drawing andexplained in greater detail in the following description. In thedrawing:

FIG. 1 shows a side view of a bicycle frame having a multi-speedtransmission;

FIG. 2 shows a shift diagram of a multi-speed transmission comprisingtwo transmission subsections and a common countershaft;

FIG. 3 shows a shift diagram of a shifting device with a rotatablecamshaft and two planetary mechanisms;

FIG. 4 shows a perspective view of one embodiment of a gear unit havingtwo transmission subsections and a common countershaft;

FIG. 5 shows an exploded perspective view of a shaft for supportingselectable free gears with a rotatable camshaft and two planetarymechanisms;

FIG. 6 shows a perspective view of a free gear with internal toothing;

FIG. 7 shows a perspective view of a selector pawl;

FIGS. 8A-F show schematic diagrams intended to illustrate shiftoperations with a rotatable camshaft;

FIG. 9 shows a perspective view of a shaft with selector pawls,rotatable camshafts and a twin planetary gear unit;

FIG. 10 shows an exploded view of two rotatable camshafts with a tappetclutch;

FIG. 11 shows a schematic sectional view of a shaft with free gears anda tappet viewed in an axial direction;

FIG. 12 shows a schematic sectional view of a gear unit having tworotatable camshafts and a twin planetary gear unit;

FIG. 13 shows an exploded view of two rotatable camshafts with twospring sleeves;

FIG. 14 shows a perspective view of a shaft with selector pawls andspring sleeves;

FIG. 15 shows an exploded view of a gear case with a multi-speed gearunit;

FIG. 16 shows a perspective view of a gear case for a multi-speedtransmission; and

FIG. 17 shows a shift diagram for a multi-speed transmission comprisinggearwheels mounted with nonpositive engagement.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a gear unit is designated in general by 10.

FIG. 1 shows a side view of a bicycle frame 12, which has a gear case14, in which the gear unit 10 is housed. In this illustration, the gearunit 10 is indicated only schematically and is designed as a compactunit, which is preferably arranged in a gear cage (not shown here).Here, the gear unit 10 is described by way of example for use with abicycle but it can also be used on other vehicles operated by muscleforce. Needless to say, the gear unit 10 can also be used for vehiclesin which muscle force is used in combination with a power unit fordriving the vehicle.

The gear unit 10 and the gear case 14 together with cranks 16 and 16′form a multi-speed transmission 18.

FIG. 2 shows a shift diagram of the gear unit 10.

The gear unit 10 has an input shaft 20 and an output shaft 22. The inputshaft 20 is designed as a through shaft. The output shaft 22 is designedas a hollow shaft. The input shaft 20 and the output shaft 22 arearranged coaxially with one another. The output shaft 22 is connectedrotationally fixed to a chain wheel 24, which forms an output member ofthe gear unit 10.

The gear unit 10 has a first transmission subsection 26 and a secondtransmission subsection 28. A plurality of driving gears 30, 31, 32, 33,34, 35 is mounted on the input shaft 20. The first transmissionsubsection 26 has a countershaft 36. Mounted on the countershaft 36 aredriven gears 38, 39, 40, 41, 42, 43. The driven gears 38 to 43 aredesigned as free gears.

The driven gears 38 to 43 can be connected to the countershaft 36 bymeans of selecting means (not shown). The driven gears 38 to 43 and thedriving gears 30 to 35 form gear pairs which have different transmissionratios, thus enabling different gear stages to be obtained byselectively connecting the driven gears 38 to 43 to the countershaft 36.

The second transmission subsection 28 has an input shaft 46. On theinput shaft 46 driving gears 48, 49, 50 are mounted. The driving gears48 to 50 are designed as free gears. The driving gears 48 to 50 can beconnected rotationally fixed to the input shaft 46 by means of selectingmeans. The driven gears 52, 53, 54 are mounted on the output shaft 22.The driven gears 52 to 54 mesh with the driving gears 48 to 50.

The intermeshing driven gears 52 to 54 and driving gears 48 to 50 formgear pairs which have different transmission ratios. The driving gears48 to 50 can be connected rotationally fixed to the input shaft 46 bymeans of selecting means (not shown), thereby forming differentselectable gear stages of the second transmission subsection 28.

The countershaft 36 of the first transmission subsection 26 is connectedrotationally fixed to the input shaft of the second transmissionsubsection 28. The countershaft 36 is preferably formed integrally withthe input shaft 46.

The driving gears 30 to 35 are each preferably connected nonpositivelyto the input shaft 20 by means of a clutch (not shown), in particularfrictionally by means of a friction clutch. The clutch is designed tolimit a torque introduced into the gear unit 10. The clutch is designedso that the connection between the input shaft 20 and the correspondingdriving gear 30 to 35 slips if a predefined or adjustable torque isexceeded. By means of such torque limitation, the overall size andweight of the gear unit can be reduced since the gear unit can bedesigned for a relatively low maximum torque.

By virtue of the fact that the first transmission subsection 26 isconnected to the second transmission subsection 28, the possibleachievable gear stages of the first transmission subsection 26 aremultiplied by the gear stages of the second transmission subsection 28.Thus, eighteen gears can be achieved by the gear unit 10 illustrated inFIG. 2.

It is furthermore conceivable for the input shaft 20 to be connectedrotationally fixed to the output shaft 22 by means of a clutch (notshown). It would thereby be possible to achieve an additional gear as adirect gear.

A shift diagram of a shifting device with a rotatable camshaft isillustrated schematically in FIG. 3. In FIG. 3, a shifting device isdesignated in general by 60.

In general terms, the shifting device 60 serves to connect free gears(not shown) mounted on a shaft 62 selectively rotationally fixed toshaft 62 by means of selecting means (not shown). The shifting device 60has a camshaft 64, which is arranged coaxially in shaft 62 and ismounted so as to be rotatable relative to the latter. Arranged at oneaxial end of shaft 62 is a speed superimposition transmission 66, whichis connected both to shaft 62 and to the camshaft 64. The speedsuperimposition transmission 66 is arranged coaxially with shaft 62. Thespeed superimposition transmission 66 is formed by a transmission stage68 and a control stage 70. The control stage 70 is connected to shaft62, and the transmission stage 68 is connected to the camshaft 64. As analternative, it is also possible for the control stage 70 to beconnected to the camshaft 64 and for the transmission stage 68 to beconnected to shaft 62. The transmission stage 68 is formed by a firstplanetary gear unit 68. The control stage 70 is formed by a secondplanetary mechanism 70. The first planetary mechanism 68 has a sun gear72, which is connected rotationally fixed to the camshaft 64. The firstplanetary gear unit 68 has planet gears 74, which are mounted on aplanet carrier 76. The planet gears 74 mesh with the sun gear 72. Thefirst planetary gear unit 68 has a ring gear 78, with which the planetgears 74 mesh. The ring gear 78 is fixed at a fixed reference point 80,preferably a gear cage or gear case (not shown), and is connectedrotationally fixed to the latter.

The second planetary gear unit 70 has a sun gear 82, which is connectedrotationally fixed to shaft 62. The second planetary gear unit 70 hasplanet gears 84, which are mounted on the planet carrier 76. The planetgears 84 mesh with the sun gear 82. The second planetary gear unit 70has a ring gear 86, with which the planet gears 84 mesh. The ring gear86 is connected rotationally fixed to a cable pulley 88, to which aBowden cable (not shown) can be attached.

The first planetary gear unit 68 and the second planetary gear unit 70are dimensioned in such a way that, when the ring gear 86 is stationaryor held fixed, the transmission ratio from shaft 62 to the camshaft 64is precisely 1, with the result that, in this case, shaft 62 and thecamshaft 64 rotate in synchronism or at the same speed. The secondplanetary gear unit 70 or control stage 70 serves to superimpose anadditional speed on the speed of shaft 62. This additional speed istransmitted via the ring gear 86 to the planet carrier 76. Owing to thefact that the planet gears 84 of the second planetary gear unit 70 andthe planet gears 74 of the first planetary gear unit 68 are connected toone another by a planet carrier 76, a total speed as the sum of thespeed of shaft 62 and of the rotation of the ring gear 86 is transmittedto the first planetary gear unit 68. The first planetary gear unit 68 ortransmission stage 68 serves to transmit the total speed to the camshaft64. The ring gear 86 is connected to the cable pulley 88 for conjointrotation so that it can be actuated by means of a Bowden cable (notshown). Here, the cable pulley 88 is rotated by a certain angle ofrotation in the direction of rotation of shaft 62 or counter to thedirection of rotation of shaft 62 in order to transmit this relativemotion to the camshaft 64. It is thereby possible to select the gears ofthe gear unit 10 by actuating the Bowden cable. The sun gear 62 ispreferably designed as part of shaft 62 or is formed integrally withshaft 62.

In an alternative embodiment, the two ring gears 78, 86 are mounted soas to be freely rotatable and are connected to one another rotationallyfixed. In this embodiment, the planet gears 74, 84 are each connected bymeans of a separate planet carrier. One of the planet carriers isconnected to the cable pulley 88 in order to transmit the rotation ofthe cable pulley 88 to the camshaft 64.

In an alternative embodiment, it is also conceivable for the sun gearsto be connected to one another rotationally fixed and to be mounted soas to be freely rotatable. In this case, shaft 62 would be connected tothe planet carrier of planet gears 84, and the camshaft 64 would beconnected to the planet carrier of planet gears 74.

FIG. 4 shows a perspective view of the gear unit 10. The gear unit 10corresponds to the shift diagram shown in FIG. 2, with elements that arethe same being designated by the same reference numerals and only thedifferences being explained here.

At the axial ends, the input shaft 20 has connecting sections 90, 92 inorder to connect cranks (not shown) to the input shaft 20 rotationallyfixed. The chain wheel 24 is mounted at one axial end of the outputshaft 22 (not shown). The chain wheel 24 is connected by means of acentral screw 94 to a connecting element (not shown) and is therebyconnected to the output shaft 22 rotationally fixed.

The countershaft 36 is arranged parallel to the input shaft 20. The freegears 38 to 43 and 48 to 50 are mounted on the countershaft 36, which isformed integrally with the input shaft 46 of the second transmissionsubsection 28. The speed superimposition transmission 66 is mounted atone axial end of the countershaft 36. The free gears 38 to 43 and 48 to50 can be connected to the countershaft 36 or selected by means of thecamshaft 64 (not shown) in combination with the selecting means (notshown), wherein the camshaft 64 can be rotated relative to thecountershaft 36 by means of the speed superimposition transmission 66.

FIG. 5 shows an exploded view of shaft 62, the camshaft 64 and the speedsuperimposition transmission 66. Elements which are the same areprovided with the same reference numerals, and only the differences areexplained here.

Shaft 62 has recesses 96, in which freewheel elements 98 or selectorpawls 98 are mounted. The selector pawls 98 are used as selecting meansin order to connect the free gears 38 to 43 and 48 to 50 mounted onshaft 62 to shaft 62 rotationally fixed. The operation of the selectorpawls 98 is explained in greater detail below.

The camshaft 64 has actuating elements 100, 101, 102, 103, 104, 105,which are each assigned to one or two of the selector pawls 98. Theactuating elements 100 to 105 each have a sliding section 108 and a cam110 or two cams 110. The sliding sections 108 are designed as roundsections, which are formed coaxially with an axis of rotation of thecamshaft 64. The cams 110 are designed as recesses on the actuatingelements 100 to 105. The recesses are designed as a level surface on theactuating elements 100 to 105, which form the shape of a secant in anaxial projection of the actuating elements 100 to 105. A connectingsection 112 is formed at one axial end of the camshaft 64. Theconnecting section 112 has a hexagon profile 112.

The camshaft 64 is assigned latching means 114. The latching means 114have a first latching member 116 and a second latching member 118. Thelatching means 114 furthermore have a spring element 120, which isarranged between the actuating element 105 of the camshaft 64 and thefirst latching member 116. The spring element 120 is preferably designedas a diaphragm spring assembly. The first latching member 116 has aninternal hexagon profile 122, which can be connected to the hexagonprofile of the connecting section 112 in a manner which preventsrelative rotation and allows axial movement. The first latching member116 is designed as a disk. Latching member 116 has at least oneprojection 124 or at least one nose 124, which projects in an axialdirection relative to the first latching member 116. The second latchingmember 118 has a cylindrical shape and is provided at one axial end, theend adjacent to the first latching member 116, with recesses 126 orgrooves 126. The second latching member 118 has at least one pin 128,which projects radially relative to the circumferential surface and, inthe assembled state of shaft 62, engages in a recess 130 in shaft 62 andconnects the second latching member 118 to shaft 62 rotationally fixed.The second latching member 118 furthermore has external toothing, whichforms the sun gear 82 of the second planetary gear unit 70. As analternative to the nose 124 and the grooves 126, the latching means 114can also be designed as spring-loaded balls.

The sun gear 72 of the first planetary gear unit 68 has an internalhexagon profile, which corresponds to hexagon profile 112. Alsoillustrated in FIG. 5 is an end element 131, which can be connected toone axial end of the camshaft 64 and supports the speed superimpositiontransmission 66 in an axial direction and preloads the first latchingmember 116, the second latching member 118, the spring element 120 andthe sun gear 72 against one another.

The actuating elements 100 to 105 of the camshaft 64 are each assignedto one of the selector pawls 98, allowing the selector pawls 98 to beactuated selectively by a rotation of the camshaft 64 relative to shaft62. In the process, the respective sliding section 108 actuates theselector pawls 98 in such a way that the associated free gear slides onshaft 62, i.e. the corresponding gear is not selected. The respectivecam 110 has the effect that the corresponding selector pawl 98 pivotsradially outward and connects the associated free gear to shaft 62rotationally fixed. The cams 110 of the actuating elements 100 to 105are each formed at different positions on the circumference of thecamshaft 64, ensuring that in each case only one selector pawl 98 isactuated or, alternatively, two or more selector pawls 98 are actuatedsimultaneously, and the corresponding free gear or one of thecorresponding free gears is connected to shaft 62 for conjoint rotation,at least in one direction of rotation. The actuating elements 100 to 105can have one or two cams 110, depending on the number of selector pawls98 associated therewith. The camshaft 64 has the hexagon profile 112 atone axial end in order to support further elements in a manner whichprevents relative rotation and allows axial movement.

The latching means 114 have the first latching member 116, which issupported on the connecting section 112 by the internal hexagon profile122 in a manner which allows axial movement. The second latching member118 is connected to shaft 62 rotationally fixed since the pin 128engages in the recess 130 in shaft 62. The recesses 126, into which thenoses 124 of the first latching member 116 can engage, are formed atdifferent angular positions on the second latching member 118. The firstlatching member 116 is preloaded in an axial direction, namely in thedirection of latching member 118, by the spring element 120. Therecesses 126 are formed in such a way on the second latching member 118that the noses 124 can engage in the recesses 126 and fix the camshaft64 in certain rotational positions relative to shaft 62. The rotationalpositions are chosen in such a way that they correspond to the definedshift states of the camshaft 64. The noses 124 and the recesses 126 areformed with beveled or rounded flanks to ensure that the first latchingmember can be moved out of the latching position by an axial movementand the camshaft 64 can be rotated relative to shaft 62 when a torque isapplied to the latching means. When a rotation is transmitted to thering gear 86 via the cable pulley 88, a torque is exerted on thelatching means 114. As a result, the first latching member 116 is movedaway from the second latching member 118 in an axial direction until thenoses 124 are moved out of the recess 126, allowing the camshaft 64 toperform a rotation relative to shaft 62. The first latching member 116is then turned relative to the second latching member 118 until thenoses 124 slide into other recesses 126 and latch into the recess 126 byvirtue of the force applied by the spring element 120. The camshaft 64can be fixed or held in precise predefined shift positions by thelatching means 114. As a result, it is possible to dispense withexternal latching devices, e.g. in a shift lever.

A selectable free gear with internal toothing is illustrated in FIG. 6and is designated in general by 132.

The free gear 132 has external toothing 134 and internal toothing 136.The external toothing 134 is formed on the outer circumferentialsurface. The internal toothing is formed on an inner circumferentialsurface of the free gear 132. The internal toothing 136 has slidingsections 138 and engagement sections 140. The sliding sections 138 areformed by surfaces created in the circumferential direction of the freegear 132. The engagement sections 140 are formed between the slidingsections 138, at an angle to the sliding sections 138.

The external toothing 134 serves to mesh with other gearwheels. Theinternal toothing 136 serves to support the free gear 132 on shaft 62and connect it to shaft 62 rotationally fixed by means of selectingmeans. The sliding sections 138 serve to support the free gear 132rotatably on shaft 62 and to slide on shaft 62. The engagement sections140 serve to enable selecting means (not shown), which will be explainedin greater detail below, to be brought into engagement with the freegear 132 and to connect the free gear 132 to shaft 62 rotationallyfixed.

A freewheel element or selector pawl for connecting the free gear 132 toshaft 62 for conjoint rotation is illustrated in FIG. 7 and designatedin general by 142. The freewheel element 142 has an actuating section144, which is formed on an underside of the freewheel element 142. Thefreewheel element 142 has respective support sections 146 on each of twolateral sections. The freewheel element 142 has an engagement section148. The engagement section 148 is formed on an opposite end of thefreewheel element 142 from the actuating section 144. The supportsections 146 are formed on opposite sides of the freewheel element 142,namely between the actuating section 144 and the engagement section 148.

The support sections 146 serve to support the freewheel element 142 on ashaft in a manner which allows it to rotate or pivot about an axis ofrotation 150. The freewheel element 142 is supported on the shaft insuch a way that the actuating section 144 faces toward the interior ofthe shaft. The freewheel element 142 is furthermore preloaded in such away by means of a spring element that, when not subjected to a load, theactuating section 144 is pivoted radially inward and the engagementsection 148 is pivoted radially outward. The actuating section 144 isdesigned to be pushed radially outward by means of the sliding section108 of the camshaft 64 in order to pivot the engagement section 148radially inward about the axis of rotation 150.

If the engagement section 148 is pivoted radially outward and projectsrelative to the shaft, it can be brought into engagement with theengagement section 140 of the internal toothing 136 of the free gear 132in one direction of rotation of the free gear 132 and thus connect thefree gear to the shaft rotationally fixed in the direction of rotation.

The freewheel element 142 furthermore has a sliding section 152. Thesliding section 152 serves to pivot the freewheel element 142 radiallyinward if the free gear is rotated relative to the shaft in a directionopposite to the direction of rotation and thus serves as a freewheel.

The actuating section 144 can have a groove which runs perpendicularlyto the axis of rotation 150 or in the direction of rotation of the shaftin order to accommodate a spring element for preloading the freewheelelement 142. This is explained in greater detail below.

The selector pawl 98 corresponds substantially to the freewheel element142, and therefore attention is drawn below to the embodiments involvingthe freewheel element 142 in respect of identical elements.

A gear change is illustrated schematically in FIGS. 8A to 8F. For thispurpose, radial sectional views through adjacent free gears 132 areshown during three phases of the gear change.

FIG. 8A shows a first of the free gears 132, the internal toothing 136of which is in engagement with the two associated freewheel elements142. The camshaft 64 has been positioned in a rotational positionrelative to shaft 62 such that the cams 110 of the camshaft 64 isarranged in the region of the actuating sections 144 of the freewheelelements 142 and can thus pivot the freewheel element 142 outward.

The second of the free gears 132, which is assigned to the next highergear stage, namely second gear, is shown in FIG. 8B. The freewheelelements 142 have been pivoted radially inward and are therefore not inengagement with the internal toothing 136 of the free gear 132. In thisrotational position of the camshaft 64, the cams 110 which are assignedto second gear are not arranged under the actuating sections 144 of thefreewheel elements 142, and the actuating sections 144 are thereforepushed outward.

If the camshaft 64 is turned, as indicated by an arrow 168, the cams 110remain under the freewheel elements 142 which are assigned to the firstof the free gears 132 and hence to first gear, as illustrated in FIG.8C, with the result that the freewheel elements 142 of first gear remainpivoted outward.

In FIG. 8D, the second of the free gears 132 is illustrated in thisrotational position of the camshaft 64 which is assigned to second gear.In this rotational position of the camshaft 64, the cams 110 which areassigned to second gear are arranged radially under the actuatingsections 144 of the freewheel elements 142 of second gear, with theresult that the actuating sections 144 pivot radially inward, and theengagement sections 148 can thus pivot radially outward. As a result,the engagement sections 148 can be brought into engagement with theinternal toothing 136 of the free gear 132. The freewheel elements 142are each assigned a spring (not shown), which preloads the correspondingfreewheel element 142 in such a way that the actuating section 144 ispressed against the camshaft 64. As a result, the engagement section 148pivots radially outward if one of the cams 110 is rotated under theselector pawl 142.

Since the higher gear stage has a lower transmission ratio, thefreewheel pawls 142 of the higher gear engage in the internal toothing136 and drive shaft 62 with a rotational speed which is greater than therotational speed of the free gear 132 of the lower gear. In this socalled intermediate state, the free gear 132 of the lower gear istherefore rotated in the opposite direction relative to shaft 62. As aresult, the sliding section 138 of the free gear 132 presses against thesliding section 152 of the freewheel element 142, with the result thatthe freewheel element 142 is deflected inward, and the first of the freegears 132 slides on shaft 62. The free gear 132 of the lower gear, i.e.first gear, is in the intermediate state in the freewheel.

FIGS. 8E and 8F illustrate the state in which second gear is fullyengaged. For this purpose, the camshaft 64 has been turned further inthe direction of the arrow 168, with the result that the freewheelelements 142 of first gear have been pivoted inward by the camshaft 64,as shown in FIG. 8E. FIG. 8F shows that the freewheel elements 142 ofsecond gear continue in engagement with the internal toothing 136because the cams 110 of second gear are arranged under the actuatingsections 144 of the freewheel elements 142.

Owing to the intermediate state, in which the freewheel elements 142 oftwo successive gears are pivoted out radially, selection under load ispossible. An idling state is furthermore avoided.

During shifting to a low gear, the sliding section 138 of the internaltoothing 136 of the lower gear first of all slides over the freewheelelements 142 in the intermediate state. Initially, the higher gearremains engaged. The freewheel elements 142 are only pivoted in anddisengaged when the load transmitted to shaft 154 via the free gear 132is reduced. In addition, the camshaft 64 must then be rotated further,pushing the actuating section 144 outward. The lower gear is thenengaged immediately because this gear is already in the intermediatestate or in the freewheeling state. An idling state is thereby avoided.

In FIGS. 8A to 8F, the camshaft 64 is shown with cams 110 situatedexactly opposite. As an alternative, it is also conceivable for the cams110 to be arranged relative to one another in such a way that only oneof the selector pawls is brought into engagement with the internaltoothing 136. This is achieved by not arranging the selector pawls 142exactly opposite on shaft 64. This enables the angle of rotation of thefree gear 132 before engagement of the actuating section 148 in theinternal toothing 136 to be reduced. In an alternative embodiment, justone selector pawl 142 is assigned to a free gear and just one cam 110 isassigned to the associated actuating element.

FIG. 9 shows a perspective assembly drawing of the elements from FIG. 5.Elements which are the same are provided with the same referencenumerals, and only the special features are explained here.

The speed superimposition transmission 66 is mounted at one axial end ofshaft 62. Here, the first planetary gear unit 68 has four planet gears84, which are mounted on the planet carrier 76. The planet gears 76 arein engagement both with the sun gear 72 and with the ring gear 78, withthe result that the planet gears 84 run around the internal toothing ofthe ring gear 78 and at the same time revolve around the sun gear 72.The ring gear 86—not shown here—of the second planetary gear unit 70 isconnected to the cable pulley 88. On the circumference, the cable pulley88 has a groove 170, in which a Bowden cable (not shown) can be fixed ormounted. The groove 170 is in the form of a spiral or formed in a spiralin the cable pulley 88. Pulling the Bowden cable turns the ring gear 86and rotates the camshaft 64 relative to shaft 62, as described above.

FIG. 10 shows an exploded view of two camshafts having a driver. Some ofthe elements illustrated in FIG. 10 correspond to the elements in FIG.5, with elements which are the same being provided with the samereference numerals and only the differences being explained here.

A second camshaft 172 is arranged coaxially with camshaft 64 and issupported within shaft 62, which is not shown. The second camshaft 172has three actuating elements 174, 175, 176. The actuating elements 174to 176 each have two sliding sections 178, 180 and two cams 182, 184.The sliding sections 178, 180 are designed as round sections, coaxiallywith an axis of rotation of the second camshaft 172. The cams 182, 184are designed as parallel surface areas on the actuating elements 174 to176 and, when the actuating elements 174 to 176 are viewed axially, formthe shape of a secant. The actuating elements 174, 175, 176 are eachoffset by 60° relative to one another.

A tappet 186 is arranged at one axial end of the second camshaft 172.The tappet 186 has a selector cylinder tappet 188, a tappet member orselector cylinder 190 and a cam plate 192. In the assembled state, theselector cylinder tappet is passed through the second camshaft 172 ormounted in the second camshaft 172 and is connected to the firstcamshaft 64 rotationally fixed. The selector cylinder tappet 188 has atappet section 194 which is arranged at an opposite axial end of theselector cylinder tappet 188 from the first camshaft 64. The tappetsection 194 is of cylindrical design, with a radial recess which forms aselector cylinder receptacle 196. In the assembled state, the selectorcylinder 190 is accommodated in the selector cylinder receptacle 196.The selector cylinder 190 is mounted in the selector cylinder receptacle196 in such a way that it can move radially. At one axial end, thecamshaft 172 has a sleeve section 198, which surrounds the tappetsection 194 circumferentially in the assembled state. The cam plate 192has a cylindrical section, the outer circumferential surface of whichforms a sliding section 200. The sliding section 200 has a cam 202,which is raised in a radial direction. In the assembled state, thesliding section 200 is surrounded circumferentially by the tappetsection 194. In the assembled state, the selector cylinder 190 slides onthe sliding section 200. The cam plate 192 furthermore has an indexingsection 204 with a plurality of recesses 206 or grooves 206. The sleevesection 198 furthermore has at least one nose 212, which projects in anaxial direction relative to the sleeve section 198. In the assembledstate, the indexing section 204 is connected to shaft 62 rotationallyfixed. Arranged between the first camshaft 64 and the second camshaft172 is a spring element 208, which preloads the second camshaft 172 inan axial direction relative to the cam plate 192. In the assembledstate, an end screw 210 is passed coaxially through the cam plate 192and connected to the selector cylinder tappet 188.

The actuating elements 174 to 176 of the second camshaft 172 are used toactuate selector pawls 98 of the second transmission subsection 28 inorder to connect at least one of the free gears 48 to 50 to shaft 62 forconjoint rotation. The camshaft 172 is mounted in a manner which allowsrotation relative to shaft 62 in order to actuate different selectorpawls 98 in different rotational positions. In this way, individual gearstages of the second transmission subsection 28 can be achieved. Theactuating elements 174 to 176 have the sliding sections 178, 180 inorder to pivot the selector pawls 98 radially inward, with the resultthat the corresponding free gear slides on shaft 62. The cams 182, 184of the actuating elements 184 to 186 serve to pivot the selector pawls98 radially outward and to connect the corresponding free gear to shaft62 for conjoint rotation.

In order to rotate the second camshaft 172, the second camshaft 172 canbe connected to the first camshaft 64 by means of the tappet 186. Theselector cylinder driver 188 is mounted coaxially in the second camshaft172 and is connected to the first camshaft 64 rotationally fixed. Inorder to connect the selector cylinder tappet 188 to the second camshaft172 rotationally fixed, the selector cylinder receptacle 196, in whichthe selector cylinder 190 is mounted in a radially movable manner, isformed in the tappet section 194. The selector cylinder 190 slides onthe sliding section 200 of the cam plate 192. By virtue of the fact thatthe cam plate 192 is connected to shaft 62 rotationally fixed, thetappet section 194 is rotated relative to the cam plate 192 during eachselecting operation, i.e. during each rotary movement of the firstcamshaft 64. When the selector cylinder 190 slides over the cam 202, theselector cylinder 190 is moved outward in a radial direction in theselector cylinder receptacle 196 and engages in a recess (not shown) inthe inner circumferential surface of the sleeve section 198, as a resultof which the camshaft 172 is taken along in rotation relative to shaft62. If the selector cylinder tappet 188 is turned further relative tothe cam plate 192, the selector cylinder 190 slides over the cam 202 andis moved inward in a radial direction toward the sliding section 200. Asa result, the selector cylinder 190 is moved out of engagement with thesleeve section 198 once the selector cylinder 190 has moved over the cam202. Consequently, the tappet 186 has the effect that, after eachrotation of the first camshaft 64 by 360°, the second camshaft 172 isrotated by a predefined angle, in this case 60°. For the gear unit 10,this means that, after the highest gear of the first transmissionsubsection 26, further rotation of the first camshaft 64 engages secondgear in the second transmission subsection 28 and simultaneously engagesfirst gear in the first transmission subsection 26. This means, in turn,that sixth gear in the gear unit 10 is followed by seventh gear. Thus,all 18 gears of the gear unit 10 can be selected in succession byrotating the cable pulley 88. This logical linking of the first camshaft64 with the second camshaft 172 allows convenient selection of all thegears in succession with just one shift lever. Needless to say, thedriver 186 can also be used in reverse, i.e. in the opposite direction,and in this way it is possible to downshift through all 18 gears byrotating the cable pulley 88.

The indexing section 204 with the recesses 206 is used to enable thenose 212 to engage in one of the recesses 206 and thus latch the secondcamshaft 172 in various rotational positions relative to shaft 62. Inorder to enable the nose 212 to slide out of the recesses 206, i.e.release the latch, flanks of the nose 212 and of the recesses 206 arebeveled or rounded, thus allowing the nose 212 to slide out of thecorresponding recess 206 when a relative torque is applied between shaft62 and the camshaft 172. For this purpose, the camshaft 172 is mountedin an axially movable manner and is supported and axially preloadedrelative to the first camshaft 64 by means of the spring element 208.

The actuating elements 174 to 176 each have two cams 182, 184. As aresult, two selector pawls 98 can be assigned to each of the free gears48 to 50 and can be actuated by the second camshaft 172. This has theadvantage that higher torques can be accepted by the second transmissionsubsection 28. The actuating elements 174 to 176 are each offset by 60°relative to one another because they each have two cams 110 and hencethe camshaft 172 is once again in a rotational position corresponding tothe initial rotational position after a rotation by 180°.

FIG. 11 shows a schematic representation of shaft 62, viewed in an axialdirection, for the purpose of explaining the tappet 186. Elements whichare the same are provided with the same reference numerals, and only thespecial features are explained here.

The sliding section 200 and the cam 202 of the cam plate 192 arearranged within the tappet section 194. The tappet section 194 isarranged within the sleeve section 198. On its inner circumferentialsurface, the sleeve section 198 has recesses 214. The sleeve section 198is arranged coaxially within shaft 62. The selector cylinder 190 isaccommodated in recess 196.

The tappet section 194 is turned relative to the cam plate 192, namelyin the direction of an arrow 216. Owing to the fact that recess 196slides over the cam 202, the selector cylinder 190 is pushed outward ina radial direction in recess 196 by the cam 202 and engages in therecess 214 in the sleeve section 198. The selector cylinder driver 188is thereby connected to the second camshaft 172 for conjoint rotationand, as a result, the rotary motion of the first camshaft 64 istransmitted to the second camshaft 172. Once recess 196 has rotated pastthe cam, the selector cylinder 190 moves radially inward toward thesliding section 200. The selector cylinder 190 is thereby moved out ofengagement with recess 214 and, as a result, the rotationally fixedconnection between the selector cylinder tappet 188 and the secondcamshaft 172 is released. As a result, the second camshaft 172 is takenalong in rotation by a certain angle of rotation during each completerevolution of the first camshaft 64. The angle of rotation here isdetermined by the size of the cam 202.

FIG. 12 shows a sectional view through the gear unit 10 along the inputshaft 20 and shaft 62. Elements which are the same are designated by thesame reference numerals, and only the special features are explainedhere. The chain wheel 24 is connected by means of the central screw 94to the output shaft 22 for conjoint rotation. The chain wheel 24 isprovided with internal toothing 218. A connection element 220 isconnected to the output shaft 22 for conjoint rotation. The internaltoothing 218 engages in a connection section 222 of the connectionelement 220, and a positive connection is thereby formed.

By virtue of the fact that the internal toothing 218 forms a positiveconnection to the connection section 222, the chain wheel 24 can bereplaced or mounted on the output shaft 22 in a simple manner by placingit thereon and fixing it by means of the central screw 94.

FIG. 13 is an exploded view of one embodiment of the gear unit shown inFIG. 10. Elements which are the same are designated by the samereference numerals, and only the differences are explained here.

In addition to the elements illustrated in FIG. 10, the gear unit shownin FIG. 13 has a first spring sleeve 224 and a second spring sleeve 226.The spring sleeves 224, 226 are of cylindrical design and each have aplurality of recesses 228, 230, which are formed in respectivecircumferential surfaces of the spring sleeves 224, 226. The recesses228, 230 are of substantially U-shaped design, with two parallel slotsin a circumferential direction and one slot in an axial direction, whichconnects the two parallel slots to one another. As a result, springelements 232 are formed between the slots on the circumferential surfacein each of the recesses 228, 230. The spring elements 232 are formedintegrally with the respective spring sleeve 224, 226. The first springsleeve 224 is assigned to the first camshaft 64. The second springsleeve 226 is assigned to the second camshaft 172. In the assembledstate of the gear unit 10, the first spring sleeve 224 surrounds thefirst camshaft 64 circumferentially and is simultaneously surroundedcircumferentially by shaft 62. In the assembled state of the gear unit10, spring sleeve 226 surrounds the second camshaft 172circumferentially and is simultaneously surrounded circumferentially byshaft 62. Thus, the spring sleeves 224, 226 are arranged or mounted onthe inner circumferential surface of shaft 62, coaxially with shaft 62.The spring elements 232 are formed in the respective circumferentialsurface of the spring sleeves 224, 226 in such a way that each of thespring elements 232 is assigned to one of the recesses 96 in shaft 62 orto a selector pawl 98. The spring sleeves 224, 226 are each connected toshaft 62 rotationally fixed.

The spring elements 232 serve to provide sprung support for the selectorpawls 98, with the result that the selector pawls 98 project relative toshaft 62 without the imposition of a force by one of the camshafts 64,172. This means that the spring force of the spring elements 232 causesthe selector pawls 98 to pivot inward in the region of the cams 110 insuch a way that the respective engagement section 148 projects radiallyoutward relative to shaft 62. The spring elements 232 ensure that theengagement sections 148 of the selector pawls 98 pivot reliably outward.By virtue of the fact that the spring elements 232 are formed by theapertures 228, 230 in the respective circumferential surfaces of thespring sleeves 224, 226, low-cost production of the spring elements 232and, at the same time, simple installation of the spring elements 232 ispossible.

The interaction between the spring elements 232 and the selector pawls98 is explained in greater detail below.

In FIG. 14, shaft 62 is shown in a perspective assembly drawing. Theillustration in FIG. 14 corresponds substantially to the illustration inFIG. 9, wherein elements which are the same are designated by the samereference numerals, and only the differences are explained here.

The selector pawls 98 correspond substantially to the selector pawl 142illustrated in FIG. 7, and therefore reference is made in this respectto FIG. 7.

The selector pawls 98 are provided with the spring elements 232, whereinthe spring elements 232 are each accommodated in a groove 234 in theselector pawls 98. To this extent, the selector pawls 98 in FIG. 14differ from the selector pawl 142 illustrated in FIG. 7. The grooves 234are formed on a section of the selector pawls 98 which can be pivotedradially inward.

The spring elements 232 exert a force on the selector pawls 98 in such away that the actuating section 144 (not shown here) is preloadedradially inward. As a result, the engagement section 148 of the selectorpawl 98 pivots outward if the corresponding cam 110, 182 is facing thecorresponding selector pawl 98. When the corresponding camshaft 64, 172is rotated further, so that the corresponding sliding section 108, 178faces the selector pawl 98, the actuating section 144 is pushed radiallyoutward, the engagement section 148 is pivoted radially inward, and thespring element 232 is subjected to a load.

FIG. 15 shows an exploded view of a gear case for the gear unit 10. InFIG. 15, a gear case is designated in general by 240.

The gear case 240 has a case shell 242, which surrounds the gear unit 10substantially circumferentially in the assembled state. The gear case240 has a first case cover 244 and a second case cover 246, which closethe case shell 242 at the axial ends thereof and accordingly form endfaces of the gear case 240. Respective case gaskets 248, 250 arearranged between the case covers 244, 246 and the case shell 242. Thecase covers 244, 246 each have an opening 252, 254 to enable therespective connecting sections 90, 92 of the input shaft 22 to be passedthrough to the outside. The connection element 220, which connects thechain wheel 24 to the output shaft 22 for conjoint rotation, isfurthermore passed through the opening 252. The connection element 220has the connection section 222, which is designed as toothing. The chainwheel 24 has the internal toothing 218, which engages in the toothing ofthe connection section 222 and connects the chain wheel 24 to theconnection element 220 rotationally fixed. The chain wheel 24 is fixedon the connection element 220 by means of the central screw 44. The casecover 246 furthermore has an opening 256, through which shaft 62 ispassed to the outside. The speed superimposition mechanism 66 is mountedat the opening 256, namely an outer side 258 of the case cover 246. Thespeed superimposition mechanism 66 is connected to shaft 62, which ispassed through the opening 256. A mechanism cover 259, which surroundsthe speed superimposition transmission 66 circumferentially and at anend facing away from the case cover 246, is fixed on the outer side 258of the case cover 246. The mechanism cover 259 has two penetrations 260,262, through which Bowden cables can be passed and accommodated in thegroove 170 of the cable pulley 88 in order to actuate or rotate thecable pulley 88.

Support elements 264, 266, 268 are assigned to the gear case 240. Thesupport elements 264, 266, 268 serve to connect the gear case 240 firmlyto the frame 12 and to support the gear case 240 on the frame 12. Thesupport elements 264, 266, 268 are preferably connected to the gear case240 by means of vibration-damping mounts 269 made, for example, ofrubber in order to form a vibration decoupling means between the gearcase 240 and the frame 12. The mounts 269 can thus prevent transmissionnoise from being transmitted without damping to the resonant elements ofthe bicycle frame 12, thus acoustically decoupling the gear case 240from the frame 12.

A perspective assembly drawing of the gear case 240 is illustrated inFIG. 16. Elements which are the same are provided with the samereference numerals, and only the special features are explained here.

The case covers 244, 246 have a plurality of screw holes 270. The caseshell 242 has a corresponding plurality of screw holes 272. By means ofthe screw holes 270, 272, the case covers 244, 246 are screwed to thecase shell 242. Moreover, the screw holes 270, 272 serve to connect thegear case 240 to the frame 12 and to the support elements 264, 266, 268.The screw holes 270, 272 can furthermore simultaneously serve formounting rear wheel suspension systems in the case of bicycles with fullsuspension.

In FIG. 17, a gear unit with nonpositively mounted gearwheels is shownand designated in general by 280. The gear unit 280 correspondssubstantially to transmission subsection 26 in FIG. 2. Elements whichare the same are designated by the same reference numerals, and only thedifferences are explained here.

Gearwheels 282, 283, 284, 285, 286, 287 are mounted on the input shaft20. The gearwheels 282 to 287 are designed as free gears and are each inmesh with the corresponding driven gears 38 to 43, which are mounted onthe countershaft 36. The free gears 282 to 287 are each connected to theinput shaft 20 by means of a clutch 290, 291, 292, 293, 294, 295. Theclutches 290 to 295 preferably connect the free gears 282 to 287 to theinput shaft 20 nonpositively. In a special embodiment, the clutches 290to 295 are designed as friction clutches and connect the free gears 282to 287 frictionally to the input shaft 20. As an alternative, one clutch290-295 or two clutches 290-295 can be provided for all the free gears282-287.

The clutches 290 to 295 are designed in such a way that the free gears282 to 287 can be connected to the input shaft 20 for conjoint rotationup to a predefined torque and slide on the input shaft 20 above thepredefined torque. This enables the torque introduced into the gear unit280 via the input shaft 20 to be limited and hence enables the gear unit280 to be designed for a corresponding maximum load. In a specialembodiment, the torque which can be transmitted via the clutches 290 to295 is adjustable. In a special embodiment, the predefined torque canfurthermore be set to a different level or individually for each of theclutches 290 to 295.

Needless to say, the clutches 290 to 295 in FIG. 17 can be combined withall the gear units of the present invention, in particular with the gearunit 10 in FIG. 2.

What is claimed is:
 1. A gear unit for a vehicle that is driven bymuscle force, having a first shaft, on which a plurality of firstgearwheels is mounted, and a second shaft, on which a plurality ofsecond gearwheels is mounted, wherein each of the second gearwheels ismeshed with a respective one of the first gearwheels, wherein the firstgearwheels are formed as free gears which can be connected rotationallyfixed to the first shaft by means of selecting devices, wherein each ofthe second gearwheels is connected nonpositively to the second shaft bymeans of a respective torque limiting clutch, wherein each of the torquelimiting clutches connects each of its associated one of the secondgearwheels to the second shaft up to a predetermined torque, and whereinthe predetermined torque is adjustable individually for each of thesecond gearwheels.
 2. The gear unit as claimed in claim 1, wherein eachsecond gearwheel is adapted to slide on the second shaft above thepredetermined torque.
 3. The gear unit as claimed in claim 1, whereineach torque limiting clutch is designed as a friction clutch.
 4. Theshifting device as claimed in claim 1, wherein the selecting devices aredesigned as selectable freewheels.
 5. The shifting device as claimed inclaim 1, wherein the selecting devices have selector pawls, which can bebrought into engagement with internal toothing of the free gears.
 6. Agear unit for a vehicle that is driven by muscle force, having a firstshaft, on which a plurality of first gearwheels is mounted, and a secondshaft, on which a plurality of second gearwheels is mounted, whereineach of the second gearwheels is in engagement with a corresponding oneof the first gearwheels and meshed with the corresponding one of thefirst gearwheels, wherein each of the second gearwheels can be connectednonpositively to the second shaft by means of a torque limiting clutch,wherein each of the torque limiting clutches connects each if itsassociated one of the second gearwheels to the second shaft up to apredetermined torque, and wherein the first gearwheels are formed asfree gears which can be connected rotationally fixed to the first shaftby means of selecting devices.
 7. The gear unit as claimed in claim 6,wherein each second gearwheel is adapted to slide on the second shaftabove a predetermined torque.
 8. The gear unit as claimed in claim 7,wherein the predetermined torque is adjustable.
 9. The gear unit asclaimed in 6, wherein the second gearwheels are formed as free gearswhich can be connected rotationally fixed to the second shaft by meansof torque limiting clutches.
 10. The shifting device as claimed in claim6, wherein the selecting devices are designed as selectable freewheels.